1. Field of the Invention
The present invention relates to a bogie for a guide rail type vehicle in which guide wheels roll along a guide rail while being in contact with the guide rail arranged along a guideway thereof so as to drive the vehicle.
2. Description of the Related Art
A new transportation system as a medium-capacity transportation using rubber tires traveling on a special guideway such as a new transit system and MRT, has become popular in recent years. This transportation system is usually fully automated. In some cases, the transportation system is equipped with guide wheels being guided on a guideway.
As one type of the new transit system, there is a vehicle which comprises a pair of front guide wheels which are connected to front rubber tires of a front part of the bogie via a steering mechanism and a pair of rear guide wheels being connected to rear rubber tires of a rear part of the bogie via the steering mechanism so as to steer the front rubber tires and the rear rubber tires by the front guide wheels and the rear guide wheels respectively. For instance, JP5-22626A discloses a vehicle of this type of the new transit system.
In this type of vehicle, the steering direction of the rubber tires has to be changed into a new direction every time the traveling direction is changed or reversed. Therefore, the vehicle is usually equipped with a forward/backward-changeover device for switching the traveling direction forward or backward and the traveling direction is changed at a terminal station by switching the forward/backward-changeover device. The switching device is complex in structure and has many wear components, which requires frequent and time-consuming maintenance.
To take measure against this, a bogie for a guide-rail type vehicle is proposed in which instead of the forward/backward-changeover device, a pair of guide frames are provided for each bogie and a pair of guide wheels are provided on each of the guide frames.
For instance, one type of the above vehicles is disclosed in Non-Patent Document 1 (March issue of “Railroad Vehicles and Technique” published in 1999, pp. 9-19) discloses a variety of vehicles of this type. The bogie comprises a pair of guide frames, each of which has two guide wheels at both ends thereof, an axle, and a suspension frame connected to the axle via a parallel link mechanism. The bogie is disposed under the vehicle via a turning bearing of a ring shape. Thus, the guide frame, the axle and the rubber tires are firmly connected and the entire bogie turns along with the guide wheels guided on a guide rail.
This type of vehicle is also disclosed in FIG. 4 of Patent Document 1, JP11-278004A and in FIG. 4 to FIG. 6 of Patent Document 2, JP2003-146204A.
The bogie disclosed in Patent Document 1 and Patent Document 2 is structured such that the guide frame, kingpins and the rubber tires are integrally coupled and the guide frame and the rubber tires rotate around the kingpin when the guide wheels receive the force in a width direction with respect to the guide rail.
The bogie disclosed in Non Patent Document 1, rotates around the turning bearing of a ring shape by the side-to-side force that the guide wheels receive from the guide rail. Thus, the load on the guide wheels is high and the durability of the guide wheels becomes short.
And, the guide frame and the rubber tires are rigidly connected and thus, the uneven surface of the guide rail can be transmitted to the rubber tires directly and the traveling performance of the rubber tires becomes worse.
Further, in the bogie disclosed in Patent Document 1 and Patent Document 2, the axle does not turn with the rubber tires and thus the weight on the turning part is light compared to the bogie disclosed in Non Patent Document 1 and thus the load on the guide wheels are reduced. However, the right and left guide frames are separately formed and connected respectively to the kingpin. Therefore, the load on the guide wheels are transmitted to the kingpin via the guide frames and the large load is loaded on the kingpin via the guide frames. Therefore, the kingpin and the bearing for supporting the kingpin are subject to breakage. When the kingpin is worn away or when there is misalignment between the kingpin and the bearing, the running stability deteriorates and the height of the guide wheels and the distance between the guide wheels in the width direction of the vehicle change, thereby requiring more maintenance of the axle.
Furthermore, when the guide wheels receive irregular external force, it can cause not only the breakage of the guide wheels and the guide frames but also the breakage of the kingpin, which is the most important component of the vehicle to operate the vehicle.
To improve the cornering performance of the vehicle, the king pin is arranged with a negative camber angle so that the bottom of the wheel is father out of the top. This causes the guide wheels to move in a vertical direction when steering and thus it is necessary to provide a greater width of the guide rail in the vertical direction of the vehicle.
Further, the movement of the guide wheels due to the uneven surface of the guide rail is directly transmitted to the rubber tires, thereby affecting the traveling of the rubber tires and making the traveling unstable. Thus, it is necessary to improve the precision of the guide rail.